Why is chloroform kept in dark coloured bottles?

Hint: The molecular formula for chloroform is ${\text{CHC}}{{\text{l}}_{\text{3}}}$. In the presence of light, chloroform gets oxidised by the oxygen in the air to form phosgene.

Complete answer:
The molecular formula for chloroform is ${\text{CHC}}{{\text{l}}_{\text{3}}}$. Chloroform is a colourless and dense liquid. it has a very strong smell. Chloroform can be used as anaesthetic, sedative when it is inhaled or ingested. Chloroform is highly volatile in nature. It can be produced by heating a mixture of chlorine and methane.
In the presence of light, chloroform $\left( {{\text{CHC}}{{\text{l}}_{\text{3}}}} \right)$ gets oxidised by the oxygen in the air. This oxidation reaction of chloroform leads to formation of carbonyl chloride or phosgene $\left( {{\text{COC}}{{\text{l}}_{\text{2}}}} \right)$. Phosgene is extremely poisonous.
The reaction is as follows:
${\text{2CHC}}{{\text{l}}_{\text{3}}} + {{\text{O}}_{\text{2}}}\xrightarrow{{{\text{Sunlight}}}}{\text{2COC}}{{\text{l}}_{\text{2}}} + {\text{2HCl}}$
Thus, to avoid the formation of phosgene, chloroform is stored away from light and air.
In dark coloured bottles, no light can enter. Thus, oxidation of chloroform to phosgene can be avoided.
Thus, chloroform is stored in closed dark coloured bottles.

Additional Information: Phosgene is used in manufacturing of plastics and pesticides.
- Phosgene is poisonous at room temperature.
- When cooled under pressure, phosgene converts to liquid which can be stored.
- Phosgene is inflammable.

Note: Phosgene is an organic compound that is highly poisonous colourless gas. Sometimes phosgene may appear as a white or pale yellow cloud. Phosgene damages skin, eyes, nose, throat and lungs.
The signs and symptoms of phosgene poisoning are: coughing, watery eyes, burning in eyes and throat, blurred vision, shortness of breath, nausea, vomiting, pulmonary edema, low blood pressure, heart failure, etc.